In a sputtering process, a substrate to be processed, such as a semiconductor wafer, is mounted in a vacuum chamber reactor filled with a gas. The gas in the reactor is subjected to electrical excitation, producing a plasma in the reactor. In a sputter etching process, ions from the plasma bombard the surface of the substrate, ejecting particles of any coating on the wafer surface. The ejected particles predominantly adhere to and coat the interior surfaces of the reactor. In a sputter coating process, a target is placed in the reactor, and ions from the plasma bombard the target, ejecting particles from the target which adhere to the wafer and the interior surfaces of the reactor.
In an inductively coupled sputtering reactor, the chamber is nonconducting. Electrical excitation is in part provided by magnetic fields generated by a helical coil formed around the outside of the chamber. The coil is separated from the chamber by a magnetically impermeable barrier wall such as a quartz jar.
A difficulty with inductively coupled sputtering of metals or other electrically conductive coatings is that particles sputtered, e.g., from the wafer, tend to form a conductive film on the inside of the chamber. If the chamber is not cleaned regularly, this film will accumulate, and the resistance of the film will be small enough that magnetic fields from the coil will induce eddy currents in the conductive film. These eddy currents will tend to oppose penetration of magnetic fields from the coil into the chamber, deteriorating plasma ignition performance, or in severe cases preventing plasma ignition altogether.
Regular cleaning or replacement of the chamber can be costly both in effort expended and in downtime. And, even regular cleaning does not prevent some performance reduction as conductive films accumulate inside the reactor. Accordingly, significant cost and performance advantages can be gained from an inductively coupled plasma sputter etching reactor which is not susceptible to plasma deterioration due to conductive film accumulation on the interior of the reactor chamber.